#include <errno.h>
#include <signal.h>
#include <sys/wait.h>
#include <unistd.h>

int system(const char* cmdstring) /* with appropriate signal handling */
{
    pid_t pid;
    int status;
    struct sigaction ignore, saveintr, savequit;
    sigset_t chldmask, savemask;

    if (cmdstring == NULL)
        return (1); /* always a command processor with UNIX */

    ignore.sa_handler = SIG_IGN; /* ignore SIGINT and SIGQUIT */
    sigemptyset(&ignore.sa_mask);
    ignore.sa_flags = 0;
    if (sigaction(SIGINT, &ignore, &saveintr) < 0)
        return (-1);
    if (sigaction(SIGQUIT, &ignore, &savequit) < 0)
        return (-1);
    sigemptyset(&chldmask); /* now block SIGCHLD */
    sigaddset(&chldmask, SIGCHLD);
    if (sigprocmask(SIG_BLOCK, &chldmask, &savemask) < 0)
        return (-1);

    if ((pid = fork()) < 0)
    {
        status = -1; /* probably out of processes */
    }
    else if (pid == 0)
    { /* child */
        /* restore previous signal actions & reset signal mask */
        sigaction(SIGINT, &saveintr, NULL);
        sigaction(SIGQUIT, &savequit, NULL);
        sigprocmask(SIG_SETMASK, &savemask, NULL);

        execl("/bin/sh", "sh", "-c", cmdstring, (char*)0);
        _exit(127); /* exec error */
    }
    else
    { /* parent */
        while (waitpid(pid, &status, 0) < 0)
            if (errno != EINTR)
            {
                status = -1; /* error other than EINTR from waitpid() */
                break;
            }
    }

    /* restore previous signal actions & reset signal mask */
    if (sigaction(SIGINT, &saveintr, NULL) < 0)
        return (-1);
    if (sigaction(SIGQUIT, &savequit, NULL) < 0)
        return (-1);
    if (sigprocmask(SIG_SETMASK, &savemask, NULL) < 0)
        return (-1);

    return (status);
}
